1. Field of the Invention
This invention relates generally to finishes and closures for containers, such as carbonated beverage containers. More specifically, this invention relates to an improved closure that acts to providing a braking effect when the closure is unscrewed from the container, and does so with minimum effect on the stripping torque between the closure and the finish portion of the container.
2. Description of the Related Technology
Conventional mating closures and bottle finish structures for carbonated beverage containers typically utilize a screw type or threaded arrangement between the closure and the finish portion. These types of screw caps are mass manufactured by injection molding and have achieved commercial success mainly in the soft drink industry, where they are applied robotically to the finish portions of filled soft drink bottles on rapidly moving filling lines.
One constraint that exists in the design of conventional screw caps is that the screw connection between the cap and the thread of the finish portion must be able to withstand a definite amount of torque, which is in excess of the amount of torque that must be applied in order to ensure a sealed fit when the cap is installed onto the container after filling. This is known as the "stripping torque." Stripping torque is affected by a number of factors, including the rigidity of the cap's threads and the supporting outer wall of the cap. The thicker the outer wall, the greater the stripping torque will tend to be. Of course, material costs will rise significantly for the manufacturer as the thickness of the outer wall is increased.
Another important factor in the design of screw-type closure caps for carbonated bottles is that of ensuring that the connection between the cap and the finish portion of the container is properly vented so as to permit compressed gases from within the container to be released gradually as the cap is unscrewed by the consumer. To achieve this, it is common for the threads of finish portions of conventional soft drink containers to be intermittent, as opposed to a continuous helix. It is also common for the internal threads of the closure caps to have periodic gas venting gaps.
To ensure that the pressurized gases are relieved before the closure is removed from the container by a consumer, techniques have also been developed to retard or brake the unscrewing of the closure cap. FIG. 1 is a developed view of an inside surface of the cylindrical wall portion of one type of closure 10 that is in commercial use. Closure 10 includes an outer wall 12 that is shown projected as if it were flat, instead of being shaped substantially as an inside curved surface of a cylinder, as it is in use. As is common, closure 10 also includes a tamper-evident (TE) strip 14 having a number of ratchet teeth 16 about its lower periphery that are oriented so as to slip over a flange of the container finish portion during fastening of the closure, but to resist removal with sufficient force that, upon attempts at removal, a frangible score 18 between the TE strip 14 and the rest of the closure 10 will rupture first. Closure 10 also has threads 20 defined in the outer wall 12, and these threads 20 have periodic venting recesses 22 defined therein.
In the closure 10 that is depicted in FIG. 1, a braking effect is achieved by means of a so-called speed bump 24, which is a portion of the outer wall 12 that is slightly raised so as to extend radially inwardly toward the threads of the finish portion of the container. During removal of the closure by unscrewing, the speed bump 24 will frictionally engage the outermost surface of a thread on the finish portion, thus imparting some resistance to the unscrewing of the closure cap that will ensure that it will take several turns of the consumer's wrist to completely separate the closure from the container.
Although closure caps of the type depicted in FIG. 1 are effective to some extent, the radial force that is imparted by the engagement of the speed bump 24 with the thread of the container finish portion tends to deform the outer wall 12 of the closure 10 radially outwardly, away from the container finish. This effect substantially reduces the stripping torque value of the closure cap on a particular container finish. This problem can be mitigated somewhat by increasing the thickness, and thus the rigidity, of outer wall 10, but at the expense of greater material cost for the manufacturer.
A need exists for an improved closure cap having braking structure that will have a less profound effect on the stripping force value of the closure than closure caps with conventional braking structure.